To further investigate human auditory motion perception, a series of experiments will be conducted in an anechoic environment, in which stimuli will be presented from stationary and horizontally moving loudspeakers. Standard psychophysical procedures will be employed in all experiments, requiring subjects to make simple button-press or adjustment responses to indicate judgments about the various stimuli presented. The experiments are designed to address three basic questions related to auditory motion perception: (1) Do humans make judgments about the motion of auditory targets based on an immediate appreciation of velocity, or rather indirectly, by detecting spatial and temporal changes (i.e., by comparing "snapshots" of a target's positions at different instants)? (2) Does the existence of a frequency-specific auditory motion aftereffect necessarily imply the existence of motion-sensitive mechanisms ("motion detectors") within the auditory system? and (3) How does the presence of a single reflection (echo) affect human perception of motion, and, conversely, to what extent is the precedence effect (suppression of information about the echo) affected by the horizontal motion of a direct sound? Results from these experiments will contribute to our understanding of how the binaural system operates under dynamic conditions, both in anechoic and echoic spaces. The basic knowledge gained from these experiments might well have important practical applications for human performance in our dynamic environment.